Generally, as a film-type photosensitive transfer material, a dry film type photosensitive transfer material (hereinafter, referred to as “a dry film photoresist”) is typically used.
Generally, the dry film photoresist, which is typically used to form printed wiring boards, printed circuit boards and IC packages, includes three layers of a support film, a photoresist layer and a cover film.
The dry film photoresist includes a negativetype dry film photoresist and a positive-type dry film photoresist according to the difference in optical mechanism therebetween. In the case of the negativetype dry film photoresist, a photocrosslinking reaction is conducted at its light exposed site, and its non-exposed site is washed out with alkali and thus a resist pattern is formed thereon. In the case of the positive-type dry film photoresist, a photodegradation reaction is conducted at its light exposed site and thus developed with alkali, and a resist pattern is formed on its non-exposed site.
In the case of the positive-type dry film photoresist, a photoresist layer includes a photosensitive compound reacted by light and an alkali-soluble, and has predetermined adhesivity because a photoresist-making solution is formed into a film.
In the dry film photoresist, a support film serves to support a photoresist layer, and enables a photoresist layer having adhesivity to be easily treated at the time of exposure of the photoresist layer. Further, in the dry film photoresist, a cover film is formed on the photoresist layer on which the support film is not formed, and serves to prevent the photoresist layer from being damaged.
According to a method of forming a pattern using a dry film photoresist, for example, a positive-type dry film photoresist, when this method is applied to a printed circuit board, first, a cover film is separated from a positive-type dry film photoresist, and then the positive-type dry film photoresist is layered on a copper clad laminate (CCL), and then the CCL layered with the cover film is exposed by irradiating it with UV using a mask having a desired pattern, and then the exposed CCL is developed by washing it with a proper solvent. Generally, exposure is conducted with a support film adhered on a photoresist layer. Therefore, in this case, since the photoresist layer and the mask are spaced apart from each other by the thickness of the support film, there is a problem of decreasing resolution.
With the densification of a printed circuit board and the advancement of semiconductor packaging technology, circuit line width is densified, and thus a film-type photodegradable transfer material having high resolution, which can be applied to such a fine printed circuit board, is keenly required.
Meanwhile, in the case of some positive-type dry film photoresists, since a solvent for forming a film remains in a phtotoresist layer, the positive-type dry film photoresist is exposed after a support film is separated therefrom. However, in this case, there is a problem in that a mask and a photoresist layer adhere to each other at the time of contact-type exposure.
Further, generally, in terms of photosensitivity, since it is advantageous to prevent a dry film photoresist from being exposed to air when a photoreaction is conducted in a photoresist layer, the dry film photoresist is exposed after a support film is separated therefrom in consideration of resolution. However, in this case, there is a problem in that photosensitivity is deteriorated.